1. Field of the Invention
The present invention relates to a method of producing a blanket belt for use in a printing machine, which is preferable to be used when producing a blanket belt disposed on an offset printing machine and the like.
2. Description of the Relevant Art
Generally, in an offset printing machine, a plate is wound around and charged onto a cylindrical printing drum, then an ink image fitted onto the plate on the printing drum is once transferred (off) to a blanket drum, and the ink image transferred to the blanket drum is printed (set) onto a printing sheet. Such a blanket drum is provided with a blanket at an outer surface thereof, and this blanket is formed as a sheet-like body of a two layer construction comprising a reinforcing layer of a cloth and the like for preventing expansion and construction, and a rubber layer made of nitrile rubber such as NBR.
On the other hand, since the blanket drum is utilized at a circumferential surface thereof, if a size of the printing plate is made large, the blanket drum becomes large, so that there is caused a large-sizing of the printing machine. Therefore, up to now, there has been also proposed in U.S. Pat. No. 5,390,597 an endless blanket belt is hung on between a pair of pulleys spaced from each other, instead of the blanket drum.
However, there are caused the following problems in a case where a general blanket fitted onto the blanket drum is applied to the aforementioned blanket belt.
At first, in a case where the blanket is charged onto the blanket drum, a thickness itself of the blanket does not come into question. However, in a case where the blanket is applied to the blanket belt, an outer surface of the blanket belt is stretched at the pulley. On the other hand, since the contraction is caused at a position except the pulley due to a reaction thereof, there is a fear that the expansion and contraction are caused on the blanket belt at the time of the printing, so that a quality of printing is degraded.
Secondly, although the movement of the blanket belt and the rotation of the pulley must coincide (synchronize) with each other perfectly, the blanket cannot be moved correctly and stably due to a slip caused between the blanket and the pulley. In this regard also, there is a fear that the quality of printing is degraded.